The purposes of this research are the investigation of the biochemical characteristics of developing central nervous system (CNS) cells in dispersed cell cultures, and the use of these cultures and sensitive biochemical tests to assess the toxicity of nervous system active drugs. We have refined several assay methods so that they can be performed in situ in the culture dishes, thus minimizing variability and tissue losses, and resulting in more accurate and efficient assays. The use of these various techniques has provided evidence that the anticonvulsants phenytoin and valproic acid cause toxic effects on developing cerebral cortical neurons, whereas diazepam and carbamazepine appear less toxic.